Have to agree with CRenee, I would consider increasing the syrup amount but avoid increasing the temp. If you aren’t scraping the syrup pan, you may be leaving quite a bit behind.
I have heard professional bakers say that the frosting will be firmer if the butter is firmer- so consider mixing the meringue and butter together when both are at about 68-69F, you can use water baths or the refrigerator on the meringue, just be sure to cover it and to whisk it occasionally after the initial cooling-while-beating period.
Lastly, I think I have noticed that the frosting can be firmer at 250 than at 248F, but if you go much above 250F it will be so firm that it will be unpleasant to eat and nearly impossible to pipe.
Good luck, hope you’ll post pics