We have 2 machines (not Robot but very similar) and we do capsicum and onions on the dice, mushrooms on the 3 blade slice and tomatoes on the 2 blade slice.
Make sure your blades are nice and sharp. We have recently replaced the dicing blades as a couple broke and they were not cutting very well. They are easy to replace and cost (in expensive Australia about $40).
The only time we find it mush for onions or caps is when the operator doesn’t put enough pressure down on the plunger, tomatoes only if they are over ripe and if they put too much pressure on the mushrooms.
To help with the “mush” we collect and store everything in stainless steel collanders and then rinse them under cold water (excpet mushrooms which are straight into plastic tubs). Capsicums need about 3 good rinses to get rid of the residue and the oil, 2 for onions and tomatoes. They are left to drain for about 5 minutes. We then place the collanders in shallow stainless dishes where any remaining liquid drips out , thus keeping the food sitting out of liquid. The collanders are covered with those cheap disposable shower caps that can be washed and renewed. Keeps everything nice and crisp.
Dave