My regia's are the same - plastered in fly cadavers.
I think a combination of leaf size, upright posture and gland sizes help ensnare prey, as my filliformis plants also seem to do fairly well with upright leaves, yet have fewer prey items on them. The large glands probably are key, as the small prey will struggle much harder to escape from a big blob of sticky mucilage! The impressive and relatively quick leaf curl response, also further ensures the prey are helplessly trapped.
Incidentally, from your picture it looks as though your regia is placed at the back of your greenhouse against the glass? This will be another factor increasing fly trapping - they will fly in and travel to the back, not realising the glass is solid and as they hang about and start to turn back, they'll find the sticky leaves in the way!