After seeing posts about the after market battery strap and the fact you can't have it and the prop guards fitted at the same time,prompted me to find a solution.
And what I have done is use a Dremel type tool to trim the sides of the battery strap and now the prop guards can be fitted at the same time.
I have an aftermarket prop guard and it works with this battery strap without issue. This battery guard without the modifications as you performed I confirm it won't fit with the DJI prop guards.
I was going to that with mine but was concerned about weakening the structural integrity of the strap to the point of bending or breaking but it looks like it works.
