You are encountering these cases:

Your application needs a minimum resolution.
Users have laptops with low resolution.
When accessing through a web browser, the screen size is smaller and the application is choppy.
Need to set a minimum resolution  different from the client's initial resolution and is higher than the resolution of the application.


You can change resolution settings as explained here:

https://docs.terminalserviceplus.com/tsplus/html-pages-and-customization


You will need to edit the index.html page

The index.html is located in Web Server root folder path.

C:\Program Files (x86)\TSplus\Clients\www


Index.html page is the default web page. It’s like a front-end Portal page with links to the connection pages which are located in \www\ folder.


This web page can be copied and renamed to allow multiple configuration and / or logon information.

For example let's copy and rename index.html into index2.html, this page will be available using this url http://localhost/index2.html


You will need to change these values:

W.dynminwidth 

and 

W.dynminheight