Thanks for the suggestion. I have taken a look at the options available from the drop-down menus in the Column Properties field (there are a lot of them !). Also I have referred to the Help. At least from the latter perspective the only clear instruction (to me) is that this is a way of setting the desireability of an outcome in terms of High and Low values. So, whilst this might reject an outcome of -1 or +101 as being unfit to meet the targets set, it would not actually influence the modelling process that could generate such numbers, I am no statistician, but I can remember from courses I took long ago that there are "special" ways of treating variables which are "bounded" - so whilst for example you might expect to find a Gaussian distribution of values either side of (for example) a solution being made up with a target of 50% concentration, if the target is changed to 100%, the distribution curve would look like one half of the normal bell curve, as its impossible (other than by measurement error) to get a value above 100%.
There may be something yet to be found in JMP on this matter, but frankly I don't find the Help very helpful - its good to have the Community as an alternative, so thanks again for pointing out this option.