An equal size Risto Rap should dive deeper than an equal sized Shad Rap. The size of the bait is the length of the body of the bait in centimeters not including the bill.
How deep a bait will dive is based on several factors.
1. Length of the bill.
2. Angle of the bill relative to the bait.
3. Line tie placement.
4. Length of the bait
5. Fluid dynamics of the bait.
6. Weight balance of the bait.
7. Line size used with the bait.
There are probably more.
Here are some genaralizations for the above 7 characteristics:
1. The longer the bill relative to the length of the body, the deeper the bait will dive. This is very dependent on #2.
2. The more in line the bill is with the bait, the deeper it will dive.
3. Generally a bait with the line tie on the bill will dive deeper than one with the line tie on the body.
4. Generally a longer bodied bait with the exact same size and angle bill will dive deeper than a shorter bait with the exact same size and angle bill.
5. Larger, fatter bodied baits will not dive as deep as more slender ones, all things else being equal. Yes, even hook size makes a difference on the same bait.
6. Some baits have counter weights in the bills which points the lure down and will get it deeper than an equal bait without the weight.
7. Generally, the thinner the line used, the deeper a bait will dive. Length of line let out trolling or cast also makes a difference to a point.