Definitely not redundant to invest in the same target date fund you have in your IRA. That's what you're SUPPOSED to do. A target date fund is a fund of funds, so it's got all the diversification you need right there, and is meant to be your only investment (if not you're just changing your asset allocation which is something you should be doing intentionally). That's the path I would take if it were me.
If/when you ever start investing in a taxable account instead of just tax advantaged you might then consider breaking up the target date so you have stock funds in taxable and bond funds in tax advantaged. This is because stock funds are typically tax efficient (mostly taxed at capital gains rates, and then mostly when you sell), while bond funds are not (interest is taxed as regular income). You don't list bond funds in your 403b, but they're probably there, and you just didn't list them? Or they're certainly available in your IRA