Don't worry about the SWR differences. The impedance of any feed-line repeats every half wavelength. Therefore reading your SWR at points a couple feet apart will show variance. What matters is what shows at the transmitter (radio). Good work!
Next project: Make the vertical portion 23 feet (+/-) and build a taped inductor at the base. Wamo, a 5/8 wave gain antenna. Enjoy!