I have certainly requested this feature but it is what it is, and behaves the way it behaves.
I think what some developers don’t realise is that when some essential features are missed, out that the navigation can be a reason not to chose a whole framework. Joe’s Foundation does have this breakpoint adjust feature (yes this is a feature of Joe’s stack) and it is such a basic requirement that when you don’t have it, that it is impossible to understand why it is not included. For really simple, sites with a small number of pages, the Foundry Nav Bar works well and is easy to create an attractive navigation, but when the number of pages or the length of the page titles grows beyond a critical size, then the Foundry Nav Bar can become a project show stopper. Trying to adjust the titles or pages or reconfigure to use drop-downs, is usually not a solution.
I haven’t dug into the CSS, but I suspect that the breakpoint is accessed many times throughout the Nav bar code and it is probably much more than one simple media query. Navigation stacks are probably the most complex stacks to create and why there still isn’t a really good one available. Ironically, Bootstrap4 has excellent navigation built in so you could try to use the core B4 code. Bear in mind that Foundry is based on an early Alpha Bootstrap version, so the code will have changed in the current final release of B4.
However, I have learnt to try to work around the Foundry Nav Bar by using a PaddyVis to hide the Nav bar when the text items reach their minimum width and then I chose another non Foundry Nav option for the smaller width sizes. This is a lot of time consuming faff for what could all be avoided if there was a user setting for the transition to mobile. Unfortunately, that is not a feature of the stack.