You may have hit the nail on the head. I don't do Mode A, but that's what I found on Mode B. 5watts just didn't hack it (small antennas at even a great portable QTH) on Mode B. That was uniformly the case for me at a number of QTHs. I added a 20 watt amp. and it works great. The 817 was used in all cases. Nobody says I'm too strong with the 20 watts!

Good luck, Tony, N2U