Ran into that issue at a couple ranges especially when getting out to 300. So my fix, since the adjustable extensions on Keeney or most others come out of the main stand tube I took a 6–12 foot paint roller extension, cut the threads off square. Drilled that end a little undersize so I could make the final fit tight. Crude but
With Keeney inserted
Which then puts my large Keeney flags up to 13 feet. Very stable once anchored meaning they wouldn’t sway in the wind like some of the more popular and expensive poles going that high
Had the same for Grahams but they went bye bye.