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

t=int(input())
while(t):
    n=int(input())
    l=list(map(int,input().split()))
    s=set(l)
    s=list(s)
    if len(s)==1:
        print(-1)
        
    else:
        maxi=max(l)
        pp=-1
        p=0
        for i in range(0,len(l)):
            if l[i]==maxi:
                if i==0:
                    if l[i+1]<l[i]:
                        print(i+1)
                        p=1
                        break
                elif i==n-1:
                    if l[i-1]<l[i]:
                        print(i+1)
                        p=1
                        break
                elif l[i]>l[i-1] or l[i]>l[i+1]:
                        print(i+1)
                        p=1
                        break
        if p==0:
            print(-1)
    t-=1
                        
    
