Can I challenge the income used on an appraisal of investment property?

Currently the property brings in 2700 per month. The appraiser believes 2400 is the market rate and used this amount. At his GRM of 90, the value is below the agreed upon price. If he uses the current 2700, it would be well above. We have tried sending in different comps but he won't budge. Can I challenge in any way? It is a 4plex. I plan in living in one of the units. This is a VA loan.