1/2 wave end-fed vertical
Try 24-28 feet instead of 43 feet.
Wayne Burdick’s recommendation is for 24-28 feet and 16 feet and this appears to have been assumption during design and simulation of inductors and capacitors in the KXAT1 for 40/30/20 metres (as per page 9 of KAT1 manual).
Also trailing radial or two somewhere between 1/8 wavelength and 1/4 wavelength on the band of operation should be strung out on the ground – one or two 16 foot wires will handle 40 metres through 20. No aditinal tuning network required.
Put the 24-28 feet radiator up just like you would a half wave end-fed – no feedline, connect it to the the centre conductor of the KX1 BNC jack – the 16 foot wire(s) go to the shell. Easy up for portable operation, and lightweight to carry.
An end fed halfwave dipole may be slightly more efiicient (if your matching network is correct) but is more picky due to the effects of surrounding objects than the wire lengths mentioned above, and that pickiness may negate any potential gains.
If you desire a halfwave radiator – you will need an extra tuning network at the end of the halfwave to bring the high impedance down to something modern tuners can handle.