Depth of a Saphir


I wanted to buy an engagement ring for my girlfriend. She likes light blue, and due to saving cost I opted for a sapphire in that color as center stone (she already prefered a sapphire over a diamond beforehand).
Now, I received two possible options with different meaussurements from my jeweler. One stone is 7.1 x 5.5 x 3.6 mm (.28" x .22" x .14") at 1.08 cts, the other one is a little bit smaller 6.9 x 5.0 x 2.8 mm (.27" x .2" x .11") at 0.72 cts (both are oval). The first one is a bit too dark for me, colorwise, and I like the other one quite well, however I am unsure if its depth is fine enough or if it is just too shallow? How does this impact the brilliancy of the stone?
Since I am not an expert I would be grateful for your advice.

Kind regards