If you want to try a new developer, my suggestion is to do so when all other variables are under control.
Also, many factors play into what you find as an Exposure Index for your chosen film. Metering technique, lighting conditions, light meter accuracy, film developer, film developing technique, lens contrast, lens shutter accuracy, water quality, bellows draw calculations, etc.
Using HP5+ I find that I get the best results with full shadow detail at EI 400 in normal contrast lighting, using modern high contrast lenses, and replenished Xtol developer. More than a stop different from your 180, and we are both correct. I know those who use it at EI 800 as 'normal' too, and Dr5 reversal process has EI 1,000 as 'normal' for HP5+. Go figure.