Michael: I also just completed the processing of a roll of FP4Plus (120) exposed at 125ISO. I used Xtol at 68 degrees diluted 1:2 for 10 1/2 minutes. Base + fog was .11 which is about where it should be for roll film. The negatives will easily print on grade 2 or 2 1/2. Agitation was constant for the first 30 minute and then for 5 inversions and rolls at each 30 seconds.(posted 9152 days ago)I don't have a reference for 70 degrees but your time of 5 1/2 minutes seems to be very short. My reference the Ilford Product Data Guide and Ilford's website.
I don't normally shoot FP4 plus. In fact this is the first roll that I have used in quite some time. I use Delta 100/400/3200 exclusively with Xtol. I have run extensive tests on the Delta films to determine proper time/temp/dilution. I would suggest that you do the same for your processing and shooting style with FP4.
Bob