It looks like you may be doing a Spring under.
Your conundrum is one of trailer axle ground clearance vs trailer frame ground clearance vs trailer coupler height vs hitch receiver height with the trailer and tow vehicle fully loaded. This is further complicated if the trailer coupler height prevents you from opening a tailgate.
1. Using tow vehicle tire size as a must forces you to build the suspension to keep all of the above level and/or to get the trailer coupler height to allow you to open a tailgate. With big tires; this would either require a spring under, flat springs, or short spring mounts.
2. Using a variable tire size that allows you to build the suspension with the maximum trailer axle ground clearance vs trailer frame ground clearance while ensuring a level trailer coupler height and hitch receiver height that will always allow you to open a tailgate. With smaller tires; this would allow either a spring over, lift springs, or tall spring mounts.
I've always built my OFF ROAD trailer suspensions based on #2 built around an even trailer coupler to hitch height. This allows me a trailer with high frame clearance, axle clearance > tow vehicle axle pumpkin clearance, and maximum suspension travel. I always start off with a spring over, then get springs, spring mounts, and tires to complete.
Case in point; my M416 had 31" tires, spring over with stock springs and shorter spring mounts, and my Neon is on 28" tires, spring over with flatter and longer springs and stock tall spring mounts to achieve the same result and with an even trailer coupler to hitch height. Both trailer's frames were at 25" and both trailer's axles were higher than the tow vehicle's pumpkin ground clearance with 35" tires.
My secondary belief on using variable tires is that mine are smaller, less weight, easier to find a spare mounting location, and are a more easily found size and cheaper to replace than the tow vehicles big tires. Yes, tires equal to the tow vehicle's results in maximum axle ground clearance and equal to that of the tow vehicles', but I still achieve over a foot with my reasoning.