I think there might be some misunderstandings here about how credit scores are derived...for example, your Income is not part of your credit report. Lenders get your income information from your credit application or they may use an estimated income.
Because it is not part of your credit report, income is not considered by credit scoring systems that use only your credit history. There are some customized credit scoring systems; however, that also pull in details from your credit application, including your income. Scores from those systems would be affected by your income. But in general, most loans and credit cards rely on what you claim your income to be. And regardless, a change in income is in no way reported.
Credit scores can drop for a number of reasons, and while under-utilization is one of them, it's a low and slow impact. I highly recommend to anyone interested in their credit, using
Credit Karma ...it's a free service I've found helpful for years. The link explains how they stay "free", and I have no problem with lending institutions sending offers.
Scores are updated every 7 days with Transunion and Equifax, and it will show you why it went up or down, and lets you see if there might be a problem you'd otherwise be unaware of.
Simply using a card and paying it off immediately via online is all it takes to avoid under-usage problems.
Taking out a personal loan for even $500 and putting it in bank, set up autopay, and let it alone is a great way to improve your score for only a few points of interest...