You are correct. The auto setting for minimum shutter speed in the auto iso setting only allows for whole stop adjustments to the reciprocal calculation. This allows of -2, -1, 0 +1 and +2 EV adjustments to the reciprocal, but not half-stop adjustments. So you could not dial in an automatic 1.5X adjustment.
I never use auto iso whenever the camera is on a tripod, because I can typically afford a long shutter speed and want to keep the camera at base ISO. But when I'm handholding the camera, I find auto iso to be very handy, and the auto minimum shutter speed makes it even hander, especially when using a zoom lens. I'm an "A" shooter, which allows me to control my depth of field. By setting a floor for minimum shutter speed, I like how the camera will then raise the iso in 1/6th stop increments to no more than is required for proper exposure. This leaves me in control of the aperture and a minimum shutter speed I'm willing to accept, and lets the camera make the calculation on the final variable, which would be shutter speed when light is sufficient, or iso when it is not.