Hi tullio0106,
Still we are unable to reproduce this scenario as described by you. Using the exact same MultilineTextBox component that you are using when the rows property is set to ‘2’ the height/size of the component is as intended.
It is possible that you are overwriting the rows value somewhere in your code that is what I would suggest.
Anyway this is how the HTML is rendered using you code:

<smart-multiline-text-box id="e497880705" class="elemento_textarea_valore smart-element smart-multiline-text-box smart-drop-down-box has-value" placeholder="Insert value" horizontal-scroll-bar-visibility="auto" vertical-scroll-bar-visibility="auto" enter-key-behavior="newLine" rows="2" value="
        " name="e497880705" drop-down-button-position="right" drop-down-open-mode="default" type="textarea" role="textbox" aria-multiline="true" aria-describedby="e497880705Hint" aria-labelledby="e497880705Label">

And the textarea:
<textarea class="smart-input" autocapitalize="none" autocomplete="off" cols="20" minlength="0" name="e497880705" placeholder="Insert value" rows="2" wrap="soft" aria-label="Insert value" smart-id="input" id="e497880705Input"></textarea>
If you can create a code example that we can reproduce the same scenario it will be the best so that we could be able to give you a solution about it.
Please, do not hesitate to contact us if you have any additional questions.
Best regards,
Yavor Dashev
Smart UI Team