Hi,
1. That's because of the banner of your template at the top which hides the top of the page. Without it, it would display just fine.
Change the code to :
<input type="hidden" name="url" value="<?php echo $this->params->get('url');?>#tm-bottom-a"/>
And that should circumvent the problem.
2. My solution was for the cart module, and you didn't ask for the add to cart up until now, so yes, that's normal that it worked only for the cart module.
For the add to cart, you want to turn on the "Use AJAX when possible for add to cart buttons" option of the HikaShop configuration.