Plenty of case airflow, no doubt there.
Pea size is way too much if you are talking about the size of a canned pea. About half of that would be appropriate.
Likely this is a bad mount. Pressure is very important so practing locking down the heatsink before applying any thermal paste is usually a good idea. Also, it is extremely important that you get ALL of the old thermal paste or thermal pad off both the CPU lid and the heatsink mating surface. Use of isopropyl alcohol is recommended. Don't scrape using anything that can scratch of mar the surfaces, simply wipe and buff using paper towels or lint free cloths damped with iso alcohol until you have totally clean surfaces.
Apply about half of a canned pea sized amount and press the heatsink straight down. Lock one corner down then move diagonally across and lock the opposing corner down. Next, lock the other two corners down. If possible continue applying medium to light pressure straight down during the entire process until all corners are fully locked down.
Make certain that the CPU fan heatsink is not filled with dust and dirt down in between the heatsink fins, if it is, it needs to be blown out or the fan needs to be removed and the heatsink washed, dried and reassembled, followed by application of the thermal paste.
Since you had a faulty TIM application you need to again clean ALL of the thermal paste from both mounting surfaces prior to mounting the HSF down again if it was removed at all after the initial attempt otherwise there WILL almost certainly be air bubbles or poor coverage of parts of the mounting surfaces.
Prior to establishing the mounting pressure you'll need to have already applied your thermal paste and although opinions regarding the correct amount vary as widely as you can imagine, the old adage about opinions being like a very distinctly distasteful body part would certainly seem to apply here. Everything from five very small dots to slathering it on with a credit card, using a pea sized dollop, the three line method and possibly anything else up to and including drawing a smiley face have been not only mentioned in various circles but almost certainly tried in reality as well.
-Some methods "Recommended" around the web-
-The likely, but undesirable results of those methods-
I don't recommend any of those, and to clarify, I'm not claiming to be an authority or trying to indicate there is no other way but mine, but it is one that has worked on literally hundreds of builds over the years without issue. I personally prescribe to the uncooked rice grain sized application when using any of the commonly available pastes that come in a tube applicator like the Arctic Silver 5 or most of the included pastes that come with premium coolers.
I've never had excess paste squeeze from between the CPU lid and heatsink using this method nor had an issue with inadequate cooling due to any lack of sufficient TIM. You can make your own decision on what works best for you. Depending on the cooler, a very small snow pea sized dab will work well too, so long as you don't get carried away or misconstrue the definition of snow pea. For our purposes, perhaps a dab about 1/3 the size of a number 2 pencil eraser is a better description.
-Probable results-Notice that even with this method there is substantial filling of the heat pipe seams. It is NOT necessary to lay multiple lines along seams.
Nearly every novice builder thinks more will be better, until they learn for themselves how wrong that way of thinking truly is. The paste is only there to provide a thermal interface between the metal of the cpu lid and the base of the heatsink. It's only job is to bridge any convex or concave tendencies of the lid or heatsink base and to fill microscopic pores in either surface.
It's not there as a magic cooling pad and it's use would actually be entirely unnecessary were both surfaces to be completely flat and non-porous. But since that is unlikely, a thermal interface material is required.
(As home mechanics, handymen, tinkerers and especially with guys in general, we tend to want to always do a little extra. An extra turn on that bolt, which causes it to break. An extra half gallon in the gas tank, which overflows and slowly eats your paint away.
The list goes on but in this instance you'll want to to avoid the inclination to add any "extra" or "just a little bit more" when applying the paste. One small strip in the dead center, the size of an uncooked grain of rice, is plenty to fill the needed areas when the heatsink is tightened to the correct specifications using the recommended tightening procedure.)
http://www.tomshardware.com/faq/id-2520482/solving-temperature-issues-hyper-212-evo.html
*One thing to note is, those recommendations are for high mounting pressure aftermarket HSF units. The stock coolers are generally a low mounting pressure arrangement, so SLIGHTLY more thermal material is recommended. About half the size of a canned pea, or two uncooked rice grains, dead center of the CPU lid, works well on low mounting pressure configurations since the lower mounting pressure does not allow as much spreading of the TIM as it does with higher pressure aftermarket coolers.