You've identified you're two problems here:
1) You land backseat (this sucks I loose many a toe nail to this)
2) You're boots don't fit
If you are not landing backseat very often then it has to be #2. Ask a bootfitter the exact same question you are asking us and he will set you straight.
Another possibility, you could try switching up socks. Go for something thinner like a compression sock. Boots fucking suck, getting them dialed is always a pain in the ass. Best of luck.