It's really tight because you didn't use the correct hardware. There always a good chance an impact socket will have clearance issues on small hardware. A ten millimeter bolt with a 12 or 13 millimeter head is hand tightened with a 3/8 or 1/4 drive regular or deep socket. When those grade 8 Allen head fill with dirt and rust won't that be fun getting them out.
Post was specifically made to mainly highlight the proper size, more than what I bought. Well aware the ones I used are not the 'correct hardware', however I prefer cap screws in situations with limited space. I'm also unwilling to pay the ridiculous amount they want for the originals, nor do I have the time to waste waiting for them to ship.
I use cap screws on my Jeep (which sees heavy off-road use) and I have never had an issue with dirt or grim in the heads. In fact Jeep uses Allen head screws all over the vehicle (transmission, t-case, diffs, etc.), as do a lot of other manufacturers and OEMs. If anything does get in there, you can clean it out with a pick and some PB blaster in a few seconds. Besides...they're going to get a thick coat of FluidFilm soon as well...doubt rust will be an issue.
The fitment part was just included as a caution/extra info, in case someone else tries it. I didn't want to use any swivels or wobbles to install (they would make it easier), yet I was still able to do it. Just used a plain old Craftsman 3/8 drive hand ratchet. Definitely didn't use an impact socket either, nor would they fit there (standard impact sockets).
The cap screws I used are metric class 12.9, which is significantly stronger than a standard grade 8 bolt. The factory bolts are actually class 10.9, which is roughly the equivalent to (slightly stronger actually) than a grade 8 bolt.