1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

l=[]
for _ in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    if len(set(a))==1:
        l.append(-1)
    else:
        m=max(a)
        maxind=0
        for i in range(n):
            if a[i]==m:
                try:
                    if a[i-1]!=m and i-1>=0:
                        maxind=i
                        break
                except:
                    None
                try:
                    if a[i+1]!=m:
                        maxind=i
                        break
                except:
                    None
        l.append(maxind+1)
for i in l:
    print(i)