Corner placement causes all the boundaries to reinforce sound so unless tuned very carefully that can be a difficult location to get right. A t-line also has a tremendous amount of output which further exasperates the issue. Did you try mid-wall anywhere? That should help
If you have only one wall then there's little choice, but without using a simulator it would be difficult to know exactly where on that wall it should be. It might be better to build standard sealed or ported subs and place them where the measurements dictate best performance.