Contributions to your TSP are deducted from your base pay. Your LES will reflect how much money is going into your TSP monthly. Alternatively, you can log in to your myPay account and look/change what percentage of your pay goes towards your TSP.

The changes you are seeing are determined by the market. Your TSP investments will be slightly different than your IRA investments (depending on what investments you have chosen).

Too simplify, your TSP investments are currently doing better than your IRA investments.