Connecting the strap to the apex of a bra can be done in several ways and there is nothing more frustrating then when the apex comes out past the bra once it's attached to the strap.
Designing a bra
There are three ways I usually attach the bra strap depending what look I'm going for.
1. Laying the strap right side face down, on the bra right side up, sewing then flipping the strap upwards so your seam is hidden and then securing the strap down. This method hides the raw edges, but can be quite bulky, and if you're sewing on a domestic machine, can cause needles to break due to the thickness of all the materials. A lesson that was repeatedly learnt when making bras for my brand Vanjo.
2. Laying the bra strap behind the apex of the bra, this method produces a less bulky finish than method one, but leaves the raw edge of the bra, unless you bar-tack over it or place a bow there.
3. Placing the strap behind the apex, and then finishing off your attachment of your elastic, so that the neck-edge and underarm elastic when turned covers the bra strap. It still leaves a raw edge on the bra but the insides of the bra is beautifully finished.
I used method one, when I made a toile of the Martha pattern (a racer back crop top), so to rectify this problem, I can either reduce the width of the pattern by 3mm, though this might turning the elastic quite tricky, heighten the pattern slightly, so when the strap gets turned its not being turned onto a thicker part of the pattern. Or I can change the method of attaching and place the strap behind the apex to create a seamless transition from bra to strap.
I think I will alter my way of attaching it on this style, also if I change the elastic width in future sewing, I won't have to alter the pattern if I do it this way.