It doesn't make sense to spend time designing touch-unfriendly elements on narrow widths for mouse users.

What about Ipads? Mobile, but also big?

Just do your user research to see if it’s worth detecting non-touch input and resize elements. If you do this, you’ll be doing it for all larger widths, not just your guess at tablet. You don’t want to do it based on device detection because so many tablet users prefer keyboard and trackpad input (but again, try to find that out for your app/site’s user base.)

Lots of “gotcha” questions being asked that are symptoms of less-than-thorough responsive and multi-device development, I have to say…