Any chance you can include a picture of the spot ? I would have thought "top corner" would still be positioned under the fiberglass overhang.
FWIW: Many years ago we patched a 3 inch "T" shaped tear in an old canvas Army tent. Put a canvas patch on both sides that were glued (cant remember what adhesive we used, but didn't have the benefit of any of the new product now in the market), We've patched many holes/tears over the years.
A guy camping next to us helped - he was brilliant! He instructed us to poke a couple small holes in the tent canvas around the tear, 4 or 5 on each side of where the patch edge would be located, but just inside the outer edge of the patch location - this was so the glue would reach the identical patch on the other side creating a strong bond - He explained "like rivets" (tent canvas would be sandwiched between the two patches on each side). Worked every well - we must have had that ten another 5 or 6 years and it never had an issue.