Dragon Beard caramel too soft I had a few attempts at making Dragon Beard candy, and I can't seem to get a handle on the consistency of the caramel.

Here's the recipe I use:

200g sugar
13g dextrose
1g lemon juice
130g water

- mix ingredients
- heat up to 135°C
- immediately remove from heat
- pour into silicone containers
- let cool until solid


Now from my understanding, there is quite a bit of chemistry involved, so the ingredients have to be measured precisely and the target temperature is very important, as it decides on the hardness of the caramel when solid. Too soft and the dragon beard will fall apart during pulling. Too hard and it will break.

I had a few previous attempts that turned out fine, so I thought I had the temperature figured out for this recipe, but recently another batch failed (too soft). I am using a digital thermometer, but it's a hand-held device, so I can't control precisely whether it touches the bottom of the pot or not, which might be a problem. 

Also I wonder whether the time until the temperature reached is important. I am aware that the temperature plateaus for a time while the sugar does its transformation thing, and then starts to go up again, but I might be losing too much water during boiling if I wait too long.

There seem to be multiple factors that could potentially fail the process, so can anyone with experience on the matter help me out? Are there any tricks I may be missing?
The time to reach the given temperature is not particularly important. When making sugar candy like this, the target temperature determines the amount of water remaining in the mixture; as long as it gets to the target temperature, it doesn't matter what it did along the way. (With one exception: If you cooked it to too high a temperature, letting it cool back down won't bring the water back.) 

It's probable that you're seeing the results of a temperature differential. I'm not sure what you mean by "it's a hand-held device, so I can't control precisely whether it touches the bottom of the pot or not" -- can't you just hold it so it doesn't? -- but if you were measuring the bottom of the pot rather than the syrup then the readings will be inaccurately high, and you're likely to get a result that's too soft.

EDIT: So, I should mention one aspect of time/temperature that might matter to some candy-making. If you were to heat a mixture of white sugar and water to 135 degrees extremely quickly, the mixture would be likely to crystallize rather than remaining as a syrup. Heating it slower would allow the sugar time to split into fructose and glucose (known as "invert sugar"), which would not crystallize. In this recipe, though, the lemon juice accelerates the inversion, and in any case the dextrose will prevent crystallization. So while there is a bit of chemistry going on, the precise measurements are not especially important and most of what's happening is just physics. (The temperature is very important.)