too tall for sure. backfill it and no problem with the leggy issue. is it 100W actual draw or is that what the company stated. if your keeping it at 4inches from the top i assume it aint actual draw cause i have a 75W stated light i had to keep it just as close to grow anything worth while. it worked but as the plant gets bigger it causes more issues like lack of lighting to lower part of the plant and lesser yields during flowering.
what lights do you have exactly? maybe people can give better answers based on that also try and state your grow room/budget maybe they can help with making DIY shit as well especially if your on the cheaper end i know people aint got tons of money to grow i been there done that and i know people on here do cool shit for cheap with lighting