Subscript and underbraces

Question

I'm trying to draw an under brace below some subscripts. The thing is that, if I do it the normal way, displays just fine, but with the subscripts letter a little big for a subscript. However, if I force the size, it becomes horribly spaced from the preceding text.

Here's the code I'm using for each case Preamble:

\ProvidesPackage{mystyle}
\usepackage[spanish]{babel} %Idioma
\usepackage[utf8]{inputenc} %Codificacion
\usepackage[T1]{fontenc}    %Para que use las formas vectoriales de las fuentes
%\usepackage{lmodern}       %Cambia Computer Modern por Latin Modern
\usepackage{mathtools}      %Paquete matemático general
\usepackage{commath}        %Funcionalidad matemática adicional, como por ejemplo, derivadas
\usepackage{hyperref}       %Links dinámicos en los capítulos y demás
\hypersetup{hidelinks}      %Configura hyperref
\usepackage{siunitx}        %Notación científica y unidades
\usepackage{cancel}         %Para tachar expresiones matemáticas
\usepackage{graphicx}       %Importar imágenes

First case

\begin{align}
 \varepsilon_{\underbrace{ijl\hdots}_{n \text{ índices}}} = 
\end{align} 

Second case

\begin{align}
  \varepsilon_{\underbrace{\scriptstyle ijl\hdots}_{n \text{ índices}}} = 
\end{align} 

Here the outputs, respectively:

(Do not worry about the overfull to the right... I'm into that)